U.S. Pat. No. 4,994,534 discloses the polymerization of sticky polymers (also referred to as elastomers) in a gas phase fluidized bed reactor at or above their softening or sticking temperature in the presence of an inert particulate material (carbon black, silica, talc, clay, and the like). U.S. Pat. No. 5,304,588 teaches that the polymer produced using this process produces a unique, non-sticky elastomeric resin particle having an outer shell composed mostly of inert particulate material (e.g., carbon black) and an inner core composed mostly of polymer. In contrast to bale-form sticky polymer produced in solution and slurry polymerizations in the absence of inert particulate material, the gas phase-produced elastomer particles are granular and free-flowing as they exit the reactor and require no post-reactor pulverizing or grinding prior to their introduction into end-use applications. The elastomer is obtained in particle form with an average particle size ranging from about 0.015 to 0.06 inches.
In contrast to other gas phase reactor produced polymers (e.g., homo- and co-polymers of ethylene and/or propylene), it has been discovered that the post-reactor handling of these elastomers is difficult. That is, other non-elastomeric gas phase reactor products require only mild treatment to remove unreacted monomers and other inert hydrocarbons dissolved in the polymer. Their low catalyst residues are readily deactivated by means of additives and do not require an extraction step.
However, gas phase produced elastomers having inert particulate material incorporated in and/or on them are more difficult to treat post-reactor because they can contain one or more dienes and inert particulate materials incorporated in the polymer matrix. For example, a sticky polymer or elastomer produced in the gas phase is much more difficult to treat post-reactor since the diene component (1) has pendant double bond is capable of cross-linking, (2) is a flammable hydrocarbon, (3) can have an unpleasant odor with a very low human detection threshold, (4) is expensive making re-use critical, (5) takes 6 to 10 times longer to desorb than do the other monomers (e.g., C.sub.2 and C.sub.3) under equivalent processing conditions. Further, post-reactor side-or by-product reactions can cause odor requiring stabilization and/or purging.
Also, it has now been discovered that the elastomeric polymer polymerized using an inert particulate material can produce fines due to inert particulate material not securely or firmly incorporated in the elastomer product. Fines are particles of inert particulate material and/or particles composed of inert particulate material and small quantities of polymer having an average diameter of less than 100 .mu.m. These fines can foul downstream processing equipment (e.g., pipes, valves, feeders, etc.) resulting in a production shutdown. Accordingly, unlike other polymers produced in the gas phase in the absence of inert particulate material, these elastomers, though rendered granular, non-sticky, and free-flowing by the above-described gas phase polymerization process utilizing inert particulate materials, now require some unique post-reactor processing in order to prevent and/or minimize the presence of fines and/or to improve the robustness of the polymer particle for intact survival during subsequent processing and end-use applications.
Additionally, elastomeric polymers are prone to gel formation due to the existence of residual diene, chloride by-products of the co-catalyst and promoter. Further, elastomeric diene based products can undergo free-radical-initiated degradation, transition-metal-catalyzed degradation, and/or acid-catalyzed degradation or other undesirable post-side reactions. Hence, there is a need to properly treat these elastomeric polymers upon exiting the polymerization reactor to prevent or minimize gel formations and to stabilize and/or prevent post-side reactions prior to packaging the final polymeric product.
Therefore, there is an on-going need for improved materials handling of these polymers upon leaving a gas phase polymerization reactor.